Semiconductor manufactured nano-structures for microbe or virus trapping or destruction

ABSTRACT

A device for isolating a microbe or a virion includes a semiconductor substrate; and a trench formed in the semiconductor substrate and extending from a surface of the semiconductor substrate to a region within the semiconductor substrate; wherein the trench has dimensions such that the microbe or the virion is trapped within the trench.

DOMESTIC PRIORITY

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 15/142,188, filed on Apr. 29, 2016, entitled“SEMICONDUCTOR MANUFACTURED NANO-STRUCTURES FOR MICROBE OR VIRUSTRAPPING OR DESTRUCTION”, which is a divisional of U.S. patentapplication Ser. No. 14/988,887, filed on Jan. 6, 2016, entitled“SEMICONDUCTOR MANUFACTURED NANO-STRUCTURES FOR MICROBE OR VIRUSTRAPPING OR DESTRUCTION”, the entire contents of which are incorporatedherein by reference.

BACKGROUND

The present invention relates to semiconductors, and more specifically,to semiconductor nanostructures.

Semiconductor materials have an electrical conductivity value that fallsbetween that of a conductor, such as copper, and an insulator, such asglass. Semiconductor materials are used in many modern electronics.Semiconductor materials may be elemental materials or compoundmaterials. Silicon, germanium, and alloys thereof, are two types ofsemiconductor materials used in many semiconductor devices.

Complementary metal oxide semiconductor (CMOS) technology is used forconstructing integrated circuits. Semiconductor manufacturing techniquesinclude various precise methods for forming nanoscale structures. CMOStechnology is used in microprocessors, microcontrollers, static RAM, andother digital logic circuits. CMOS designs may use complementary andsymmetrical pairs of p-type and n-type metal oxide semiconductor fieldeffect transistors (MOSFETs) for logic functions.

SUMMARY

According to an embodiment, a device for isolating a microbe or a virionincludes a semiconductor substrate; and a trench formed in thesemiconductor substrate and extending from a surface of thesemiconductor substrate to a region within the semiconductor substrate;wherein the trench has dimensions such that the microbe or the virion istrapped within the trench.

According to another embodiment, a device for isolating a microbe or avirion includes a first semiconductor layer having a first trenchextending from a first surface to a second surface of the firstsemiconductor layer; a second semiconductor layer having a second trenchextending from a first surface to a second surface of the secondsemiconductor layer, the second trench having a diameter that is smallerthan the first trench; and an elongated gap positioned between portionsof the first semiconductor layer and the second semiconductor layer.

Yet, according to another embodiment, a device for damaging ordestroying a microbe or a virion includes a semiconductor substrate; andan array of protrusions having nanoscale dimensions extending from thesemiconductor substrate; and wherein the microbe or the virion isdamaged or destroyed after being disposed on the array of protrusions.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIGS. 1-4B illustrate structures and methods of trapping microbesaccording to an embodiment embodiment, in which:

FIG. 1 illustrates a method for using holes (trenches) in asemiconductor substrate to trap a microbe/virion;

FIGS. 2A, 2B, and 2C illustrate patterned hole arrays of differentdimensions;

FIGS. 3A and 3B illustrate a method of using a patterned hole array todetermine microbe/virion concentration;

FIGS. 4A and 4B illustrate using a roughened nanosurface for trapping amicrobe/virion;

FIG. 5 illustrates a method for size filtering microbes/virionsaccording to another embodiment;

FIGS. 6A-9 illustrate methods of making nanoscale protrusions todamage/destroy a microbe/virion according to embodiments, in which:

FIGS. 6A, 6B, 6C, and 6D epitaxial growth on fins to create an array ofnanospikes/needles;

FIG. 7A illustrates a small dimension array of nanospikes;

FIGS. 7B and 7C illustrate a large microbe/virion positioned on a smalldimension array of nanospikes;

FIG. 7D is a large dimension array of nanospikes puncturing a largemicrobe/virion;

FIG. 7E is an array with nanospikes having different sizes;

FIG. 7F is an array of nanospikes illustrating different spacing anddepths;

FIG. 7G is an array of blunt nanospikes;

FIG. 7H is an array of rod-shaped nanospikes;

FIGS. 8A-8E illustrate methods of making nanospikes, in which:

FIG. 8A is a cross-sectional side view of a photoresist and hard maskdisposed on a substrate;

FIG. 8B is a cross-sectional side view after patterning the photoresist;

FIG. 8C is a top view of FIG. 8B;

FIG. 8D is a cross-sectional side view after rotating the substrate andperforming a second patterning process;

FIG. 8E is a cross-sectional side view after recessing the substrate;

FIG. 8F is a cross-sectional side view after performing acrystallographic etch;

FIG. 8G is an electron micrograph image of a hydroxide etched substrate;and

FIG. 8H is a cross-sectional side view after removing the remaining hardmask to form the array of nanospikes; and

FIG. 9 illustrates a method for forming a flexible tube with an array ofnanospikes.

DETAILED DESCRIPTION

Semiconductor manufacturing techniques may be used to createprecision-constructed nanostructures on the same scale as pathogenicorganisms, for example, viruses and bacteria. By tuning the size andshape, the nanostructures may be used to trap, measure, physicallyfilter, or attack and destroy the pathogens. Using such methods, thepathogens may not be prone to develop resistance.

Accordingly, various methods for trapping, measuring, filtering, andattacking pathogens are described herein. The disclosed methods reducethe risk for pathogens developing antibiotic resistance. In someembodiments, a size-based trapping/filtering mechanism is described. Inother embodiments, a spike-like envelope puncture mechanism is used.Like reference numerals refer to like elements across differentembodiments.

The following definitions and abbreviations are to be used for theinterpretation of the claims and the specification. As used herein, theterms “comprises,” “comprising,” “includes,” “including,” “has,”“having,” “contains” or “containing,” or any other variation thereof,are intended to cover a non-exclusive inclusion. For example, acomposition, a mixture, process, method, article, or apparatus thatcomprises a list of elements is not necessarily limited to only thoseelements but can include other elements not expressly listed or inherentto such composition, mixture, process, method, article, or apparatus.

As used herein, the articles “a” and “an” preceding an element orcomponent are intended to be nonrestrictive regarding the number ofinstances (i.e. occurrences) of the element or component. Therefore, “a”or “an” should be read to include one or at least one, and the singularword form of the element or component also includes the plural unlessthe number is obviously meant to be singular.

As used herein, the terms “invention” or “present invention” arenon-limiting terms and not intended to refer to any single aspect of theparticular invention but encompass all possible aspects as described inthe specification and the claims.

As used herein, the term “about” modifying the quantity of aningredient, component, or reactant of the invention employed refers tovariation in the numerical quantity that can occur, for example, throughtypical measuring and liquid handling procedures used for makingconcentrates or solutions. Furthermore, variation can occur frominadvertent error in measuring procedures, differences in themanufacture, source, or purity of the ingredients employed to make thecompositions or carry out the methods, and the like. In one aspect, theterm “about” means within 10% of the reported numerical value. Inanother aspect, the term “about” means within 5% of the reportednumerical value. Yet, in another aspect, the term “about” means within10, 9, 8, 7, 6, 5, 4, 3, 2, or 1% of the reported numerical value.

As used herein, the term “microbe” means a microorganism, for example, abacteria or an archaeon.

As used herein, the term “virion” means a viral DNA or RNA core with aprotein coat, and optionally an external envelope.

Turning now to the Figures, FIGS. 1-4B illustrate structures and methodsof trapping (isolating) microbes/virions according to an embodiment.FIG. 1 illustrates a method for using holes 120 (trenches) in asubstrate 101 to trap a small microbe/virion 130. The substrate 101 mayinclude a semiconductor material, a dielectric material, or anycombination thereof. The size of the substrate 101 depends on theparticular application and targeted microbe/virion 130.

Non-limiting examples of semiconductor materials include Si (silicon,including polysilicon), strained Si, SiC (silicon carbide), Ge(germanium), SiGe (silicon germanium), SiGeC (silicon-germanium-carbon),Si alloys, Ge alloys, III-V materials (e.g., GaAs (gallium arsenide),InAs (indium arsenide), InP (indium phosphide), aluminum arsenide(AlAs)), or any combination thereof. Other non-limiting examples ofsemiconductor silicon-on-insulator (SOI) substrates with buried oxide(BOX) layers.

Non-limiting examples of dielectric materials include dielectric oxides(e.g., silicon oxide), dielectric nitrides (e.g., silicon nitride),dielectric oxynitrides, or any combination thereof.

After forming the substrate 101, optionally, a microbe/virion bindingmaterial 110 is disposed on the substrate 101. The microbe/virionbinding material 110 may be a material that has an affinity for themicrobe/virion 130 of interest. In some embodiments (not shown), themicrobe/virion binding material 110 may be disposed in the holes 120.

An additional layer 102 may be disposed on the substrate 101 to form theholes 120. Or the holes 120 (apertures/trenches) may be formed directlyin the substrate 101. The additional layer 102 may be the substrate 101material or another semiconductor and/or dielectric material.

The holes 120 may be formed in the substrate 101 or the additional layer102 by performing lithography and etch process. The etch process may bea wet etch process or a dry etch process, for example, a reactive ionetch (RIE) process. The size of the holes 120, for example, the width111 and depth 112, may generally vary and depend on the microbe/virion130 that is targeted. For some microbes/virions 130, deeper trenches maymore easily trap the target. The depths of the holes 120 may be, forexample, up to 200 nm. The diameters of the holes 120 may become smaller(more narrow), as the depth increases.

The microbe/virion 130 may be for example, a bacterium, an archaeon, orother pathogen. The microbe/virion 130 will be trapped within the holes120 after a solution or sample including the microbes/virions 130 isdisposed on the surface of the semiconductor structures comprising theholes 120. The microbes/virions 130 then become trapped within thetrenches.

The size of the holes 120 may generally vary and depend on the targetedmicrobe/virion. In some embodiments, the holes 120 have an averagediameter in a range from about 70 to about 700 nm. In other embodiments,the holes 120 have an average diameter in a range from about 70 to about150 nm.

In an exemplary embodiment, a 150 millimeter (mm) radius wafer may beused as the substrate. The 150 mm wafer has a surface area of about0.0707 meters² (m²), but only about half of the surface area may be suedto trap virions. An array of holes is formed in the substrate to trap avirus, for example, a poliovirus having about a 30 nm diameter. About1.2e6 virions may be captured per wafer.

In another exemplary embodiment, the array of holes may be used as avirus strainer with a tuned pore size. Microelectronics processingmethods may be used for precise channel size control.

In yet another exemplary embodiment, perpendicular double patterning maybe used to form the holes. Deeper vertices and/or larger vertices withinthe substrate may allow virions to enter the substrate.

FIGS. 2A, 2B, and 2C illustrate patterned trench/hole arrays ofdifferent dimensions. FIG. 2A shows a microbe/virion 230 trapped withina hole 220 in a substrate having a diameter of about 105 nm. FIG. 2Bshows a microbe/virion 230 trapped within a hole 220 having a diameterof about 64 nm. FIG. 2C shows a microbe/virion trapped within a hole 220having a diameter of about 42 nm.

FIGS. 3A and 3B illustrate a method of using a patterned hole (trench)array to determine microbe/virion concentration. The patterned arraysmay be used to quickly and easily determine microbe/virionconcentrations. FIG. 3A shows arrays 301, 302, 303, 304 of holes 320having different average sizes/diameters. A sample substrate/slide isprepared with various arrays of holes. The arrays 301, 302, 303, 304 areformed in different sections on a single substrate/slide. Differentsized holes formed on different parts of the substrate/slide may be usedto study different sized microbes/virions 330.

The substrate/slide is exposed to an environment that includesmicrobes/virions 330 (e.g., using a solution including themicrobe/virion), and the microbes/virions 330 are trapped within theholes 320, as shown in FIG. 3B. A solution may include differentmicrobes and/or virions. The surface of the substrate/slide may berinsed to remove excess particles.

The microbes/virions 330 may be labeled with a fluorescent marker sothat a black box and camera may be used to record fluorescenceintensity. The fluorescence intensity will be directly proportional tothe labeled microbe/virion 330 concentration in the holes 320. If theconcentration is too high (or at the maximum level of detection), a moredilute solution of the microbe/virion 330 may be used until a measurableconcentration is achieved. The microbes/virions 330 also may be studiesusing other analytical methods. Using arrays of holes to conduct assaysas described is fast, inexpensive, robust, and size selective.

FIGS. 4A and 4B illustrate using a roughened semiconductor nanosurfacefor trapping a microbe/virion 430. The roughened nanosurface shown inFIG. 4B may be formed by, for example, growing a high % germanium (Ge)epitaxial silicon germanium (SiGe) film on a silicon substrate. The SiGefilm is annealed to form nanoscale Ge agglomerates 421. Elongatedtrenches 420 are formed between the Ge agglomerates 421 to form theroughened nanosurface. Optionally, the roughened nanosurface may becoated with an anti-microbial material, for example, copper.

The microbe/virion 430, shown in FIG. 4A, is trapped within theelongated trenches 420, as shown in FIG. 4B. The roughened nanosurfacemay be used to trap microbes/virions 430 with elongated shapes. Theroughened nanosurface increases interactions between the substratesurface and the microbe/virion 430, which results in moremicrobes/virions 430 being trapped (or destroyed).

FIG. 5 illustrates a method for size filtering/isolatingmicrobes/virions 530 according to another embodiment. Structures forsize filtering may be formed using multiple semiconductor layers 501,502 with different sized holes 510, 511. Multiple patterning and etchingsteps may be used to create holes 510, 511 and fluid gaps 550 (elongatedgaps/trenches) between the layers 501, 502. Any number of layers andholes of any dimension may be used. The sequential layers may includedifferent sized holes to filter out different sized microbes/virions530.

A solution of the microbes/virions 530 is disposed on the first layer501 of the semiconductor structure. The first layer 501 includes holes510 with diameters that are larger than the holes 511 in the secondlayer 502. The solution may include different sized microbes/virions530. Microbes/virions 530 are large enough to pass through the holes 510in the first layer 501, but are too large to pass through the holes 511in the second layer 502 will be filtered through the fluid gap 550between the first and second layers 501, 502. The microbes/virions 530will exit (be expelled) between the layers and can be collected.Purified fluid, or fluid with smaller microbes/virions that may passthrough the holes in the next layer (holes 511), will travel through thesecond layer 502 and exit the holes 511 in the second layer 502. Thesemiconductor structure may include other layers beneath second layer502, as well as a second fluid gap beneath second layer 502 so thatother particles are expelled from a different output area in thestructure.

According to another embodiment, spikes (protrusions) of nanometer sizeddimensions (nanospikes or nanoneedles) may be used to damage/destroymicrobes/virions according to a third embodiment, which is described inFIGS. 6A through 9 below. The size of the nanospikes (nanoprotrusions)may depend on the size of the targeted microbe/virion. A solutioncomprising the microbe/virion is disposed on a surface of the array ofprotrusions to damage/destroy the microbe/virion. The nanospikes mayhave any size/dimension, and for example, may have sharp/blunt ends.

FIGS. 6A, 6B, 6C, and 6D show epitaxial growth on fins (protrusions) tocreate an array of nanospikes. The nanospikes may be formed by, forexample, forming epitaxial growth on semiconductor fin structures (e.g.,FinFET fins). As shown in FIG. 6A, fins 601 are patterned in asemiconductor substrate material. The epitaxial growth process may be,for example, chemical vapor deposition (CVD) (liquid phase (LP) orreduced pressure chemical vapor deposition (RPCVD), vapor-phase epitaxy(VPE), molecular-beam epitaxy (MBE), liquid-phase epitaxy (LPE), metalorganic chemical vapor deposition (MOCVD), or other suitable processes.The epitaxial growth process creates a diamond-shaped epitaxial growth602 on surfaces and sidewalls of the fins 601, as shown in FIGS. 6A, 6C,and 6D. The epitaxial growth process may be controlled to create spikesof different sizes, as shown in FIG. 6C. Larger nanospikes may becreated by merging two adjacent epitaxial growths, as shown by the largemerged epitaxial growth 610. Larger or smaller nanospikes may be formed,depending on the targeted microbe/virion.

The dimensions and density of the nanospikes is chosen based on thetargeted microbe/virion size. The poliovirus has a diameter of about 30nm. An Escherichia coli is about 0.5 micron×2 microns. A human cell isabout 10-100 microns in size.

FIG. 7A illustrates an array of nanospikes 702 in which smallermicrobes/virions 730 may be positioned between the individualnanospikes. FIGS. 7B and 7C illustrate a large microbe/virion 731positioned on a small dimension array of nanospikes 702. The smalldimension array of nanospikes 702 may not puncture a largemicrobe/virion 731 and may have a “bed of nails” effect. FIG. 7D is alarge dimension array of nanospikes 702 puncturing a largemicrobe/virion 731. Smaller microbes/virions 730 are not punctured andfall between the nanospikes 702. Therefore, the nanospikes 702 onlydamage/destroy a specific size range of microbes/virions.

FIG. 7E is an array with nanospikes 702 having different sizes. Thefractal pattern of spike sizes may be used for a broad range ofmicrobe/virion size destruction, as shown for small microbe/virions 730and large microbe/virions 731. The spacing 710 and depth 711 of thenanospikes 702 may also be altered, depending on the size of the target,as shown in FIG. 7F. Nanospikes 702 may have different shapes, and maybe, for example, blunt nanospikes (FIG. 7G) or rod-like (cylindrical)nanospikes (FIG. 7H).

FIGS. 8A-8E illustrate methods of making nanoprotrusions (nanospikes)according to some embodiments. FIG. 8A is a cross-sectional side view ofa photoresist 802 and hard mask 803 disposed on a substrate 801. Thesubstrate 801 may include a semiconductor material. Non-limitingexamples of semiconductor materials include Si (silicon, includingpolysilicon), strained Si, SiC (silicon carbide), Ge (germanium), SiGe(silicon germanium), SiGeC (silicon-germanium-carbon), Si alloys, Gealloys, III-V materials (e.g., GaAs (gallium arsenide), InAs (indiumarsenide), InP (indium phosphide), aluminum arsenide (AlAs)), or anycombination thereof. Other non-limiting examples of semiconductorsilicon-on-insulator (SOI) substrates with buried oxide (BOX) layers.The substrate 801 may be formed using, for example, chemical vapordeposition (CVD) (liquid phase (LP) or reduced pressure chemical vapordeposition (RPCVD), vapor-phase epitaxy (VPE), molecular-beam epitaxy(MBE), liquid-phase epitaxy (LPE), metal organic chemical vapordeposition (MOCVD), or other suitable processes.

The hard mask 802 may be an insulating material, silicon nitride (SiN),SiOCN, SiBCN, or any combination thereof. The hard mask 802 may beformed using a deposition method, for example, a CVD method or aphysical vapor deposition (PVD) method. The photoresist 803 may be, forexample, a polymeric spin-on material or other polymeric material.

FIG. 8B is a cross-sectional side view after patterning the hard mask802 and removing the photoresist 803. The photoresist is exposed to adesired pattern of radiation, and the exposed photoresist is developedwith a resist developer to provide a patterned photoresist. At least oneetch is employed to transfer the pattern from the patterned photoresist803 into the hard mask 802 and to form gaps 810 (trenches) between hardmask pillars 811. The etch process may be a dry etch and/or wet etchprocess. After transferring the pattern, the patterned photoresist 803is removed utilizing resist stripping processes, for example, ashing.FIG. 8C is a top view of FIG. 8B, showing that elongated “stripes” ofthe hard mask 802 are formed.

FIG. 8D is a cross-sectional side view after rotating the substrate 801about 90 degrees and performing a second patterning and etch process, asdescribed above for FIGS. 8A-8C. A second photoresist layer may be used,but is not necessary. A single photoresist may be used for the first andsecond patterning processed, for example, by a single resist doublelithographic (or patterning) process. The second patterning processforms an array of individual scattered cube-like structures of the hardmask 802. Additional patterning (e.g., sidewall image transfer) andetching processes may be employed to form cube-like structures havingsmaller dimensions.

FIG. 8E is a cross-sectional side view after, optionally, recessing thesubstrate 801 to form trenches 820 beneath the hard mask 802. Recessingthe substrate 801 creates will create a sharper tip in the finalnanospike.

FIG. 8F is a cross-sectional side view after performing acrystallographic etch on the substrate trenches 820 to form inversepyramid-shaped trenches 821. The crystallographic etch may be, forexample, a crystallographic hydroxide etch. The hydroxide etch mayinclude, for example, NH₄OH, KOH, tetramethylammonium hydroxide (TMAH),tetraethylammonium hydroxide (TEAH), or a combination thereof. The etchprocess may be a timed etch process or an over-etch process.

The inverse pyramid-shaped trenches 821 are formed due to different etchrates on different crystal planes in the substrate 801. FIG. 8G is anelectron micrograph image of a hydroxide etched substrate having inversepyramid-shaped trenches 821.

FIG. 8H is a cross-sectional side view after removing the remaining hardmask 802 material to form the array of nanospikes 840 in the substrate801.

FIG. 9 illustrates a method for forming a flexible tube 910 with anarray of nanospikes. The array of nanospikes extends into the center ofthe tube. A substrate sheet of nanospikes 901 is converted to a flexiblefilm 902. The flexible film may be formed by, for example, performing aspalling process, for example, with nickel (Ni). The flexible film 902may be inserted into another tube or capillary array to form a lining.Force, demonstrated by arrows 920, may be applied to constrict thepassage between the flexible films 902 and bring more microbes/virionsper unit volume into contact with the nanospikes. In other embodiments(not shown), the flexible film 902 may be rolled into the shape of atube.

As described above, various embodiments provide methods for isolating,trapping, measuring, filtering, and attacking pathogens are describedherein. The disclosed methods reduce the risk for pathogens developingantibiotic resistance. In some embodiments, a size-basedtrapping/filtering mechanism is described. In other embodiments, aspike-like envelope puncture mechanism is used.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, element components,and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

The diagrams depicted herein are just one example. There may be manyvariations to this diagram or the steps (or operations) describedtherein without departing from the spirit of the invention. Forinstance, the steps may be performed in a differing order or steps maybe added, deleted or modified. All of these variations are considered apart of the claimed invention.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A method for damaging or destroying a microbe ora virion, comprising: forming an array of semiconductor protrusionsextending from a surface of a semiconductor substrate, the semiconductorprotrusions comprising nanospikes, the array of semiconductorprotrusions having nanoscale dimensions, the array of semiconductorprotrusions comprising a fractal pattern of spike sizes; and disposingthe microbe or the virion on the array of protrusions.
 2. The method ofclaim 1, wherein the microbe or the virion is damaged or destroyed afterbeing disposed on the array of protrusions.
 3. The method of claim 2,wherein the nanospikes puncture the microbe or the virion.
 4. The methodof claim 1, wherein the nanospikes comprise a rod shape.
 5. The methodof claim 1, wherein the semiconductor substrate is a flexible film. 6.The method of claim 5, wherein the flexible film is formed into atubular shape, and the array of protrusions extend into a central regionof the tubular shape.
 7. The method of claim 1 further comprisingforming a diamond-shaped epitaxial growth on a terminal end of eachsemiconductor protrusion of the array of protrusions.